Vinyl polymers are obtainable via free-radical-initiated polymerization of ethylenically unsaturated monomers, and are mostly solid at room temperature. However, many applications require vinyl polymers in the form of solutions in liquid, polymerizable monomers (reactive monomers), an example being styrene. Solid vinyl polymers therefore first have to be converted to the actual usage form, and by way of example this can be achieved via dissolution in reactive monomers, for example as described in DE-A 102006012200 or DE-A 102006019686. For the dissolution process, solid vinyl polymers, usually in powder form or in the form of granules, are added to the reactive monomers. The dissolution process therefore represents a separate operation that consumes resources and that requires appropriate equipment. Furthermore, preventive measures have to be taken to avoid dust explosions.
As an alternative, it is also possible to melt solid vinyl polymers and to add them in the molten state to the reactive monomers. This procedure, too, requires resources in the form of apparatus, an example of the appropriate equipment required being a melting unit and a dissolution vessel. Care also has to be taken that introduction of the polymer melt does not heat the reactive monomers to an extent that results in thermally initiated polymerization; this poses enormous safety problems and can moreover require implementation of waste-disposal measures for the entire batch.
Particular problems are raised by the production of appropriate solutions of vinyl polymers with low glass transition temperatures Tg (e.g. Tg≦35° C.), because vinyl polymers with low glass transition temperatures Tg tend to cake or agglutinate at room temperature and cannot be stored in the form of powder or granules without cooling or addition of antiblocking agents. Vinyl polymers with low glass transition temperatures Tg are therefore generally marketed in the form of blocks (e.g. 25 kg blocks). However, the production of solutions via dissolution of these blocks is time-consuming and requires large-dimension dissolution equipment with high mechanical stability, because the surface area of the blocks is small in comparison with that of corresponding powders or granules. Comminution of the blocks is in practice difficult, because vinyl polymers with low glass transition temperatures Tg are tough materials. If vinyl polymers with low glass transition temperatures Tg are melted and the hot melt is added to the reactive monomer, the problems described above are again encountered. The use of vinyl polymers in the form of blocks is therefore an inflexible process in terms of batch size and is attended by considerable problems in the preparation process.